Advances in the Casimir Effect , M. Bordag , G. L. Klimchitskaya ,
U. Mohideen , and V. M. Mostepanenko
Oxford U. Press, New York, 2009. $150.00 (749 pp.). ISBN 978-0-19-923874-3
Interest in the Casimir force—the attraction between two uncharged plates resulting from the zero point energy in the vacuum between them—is greater now than ever before, in part due to the force’s role in the physics of micro- and nano-electromechanical devices. However, despite major advances in experimental techniques and calculational methods, experts still dispute such issues as the accuracy with which the force can be measured and calculated.
In Advances in the Casimir Effect, theorists Michael Bordag, Galina Klimchitskaya, and Vladimir Mostepanenko and experimentalist Umar Mohideen seek to provide a critical analysis of those controversies. In general, the authors, who collectively have more than half a century of professional experience in the field, aim to give a comprehensive review of the force that Hendrik Casimir predicted more than 50 years ago.
As an experimentalist in the field, I was looking forward to reading Advances in the Casimir Effect; I was expecting a clear exposition of the authors’ viewpoints, compared to others, on the points of contention. But I was left disappointed. This poorly edited book largely focuses on the authors’ own papers; rare acknowledgments of others are often just to point out that they are wrong.
On the whole, the authors’ analysis of the controversies is incomplete and often inaccurate. Concerning the measurement accuracy question, perhaps a dozen groups worldwide are actively measuring the Casimir force. Only two, one involving the authors, have claimed a 1% level of agreement between theory and experiment. No other group has been able to achieve anywhere near that level. My own 1997 demonstration experiment achieved 5% accuracy; at least that’s what I believed at the time.
I was subsequently proven wrong, and recent studies of background electrostatic effects suggest further corrections that would make the accuracy of my demonstration no better than 10%. In fact, some studies have shown it is impossible to control the parameters of an experiment to obtain accuracy better than 20%. I and many other experimentalists agree that the issue of how to compare theory and experiment remains open for debate. But in attempting to defend their results, the authors of this book, none of whom have a serious background in precision measurement techniques, present a useless and logorrheic discussion.
Another controversy involves the thermal correction to the so-called transverse electric field modes that contribute to the Casimir force. In 2000 Bo Sernelius’s group at the Linköping University in Sweden showed that using the Drude model of a metal’s permittivity leads to a factor of 2 reduction of the Casimir force at large separations. Initially, I rejected that result as entirely incompatible with my experiment, but now I am not so sure. However, the authors remain adamant that Sernelius and company are incorrect, a stance that seems motivated solely by the incompatibility of the Sernelius work with the authors’ 1% claim. The authors argue that Sernelius’s correction violates the third law of thermodynamics because the force associated with the transverse electric modes increases with decreasing temperature. As a consequence, they say, energy (heat) would flow into the electromagnetic field, which suggests nonzero entropy at 0 K. However, such energy flow is not unprecedented, and apparent violations of the third law are resolved when the complete system is considered. Hopefully later editions of the book will streamline much of the repetitive discussion of the transverse electric mode issue and elaborate on the role of the third law.
The book’s general incompleteness is startling, given that the body of the text runs to 701 pages. Much recent progress is missing, particularly with regard to the new numerical calculation techniques based on the fluctuation-dissipation theorem in the time domain. Lessening the book’s usefulness is a weak subject index and the lack of an author index, which is normally expected when the author/date method of referencing is employed. Advances in the Casimir Effect cannot be considered up-to-date, nor can it be taken as a scholarly review of the field, since it merely rehashes the authors’ own views. And although the book’s intended audience includes advanced graduate and undergraduate students, I expect only experts will be able to draw anything from it.
